Household appliances for cooking under pressure, of the pressure cooker kind, are well known.
They serve to provide a hermetically sealed enclosure within which food is placed, said enclosure being capable of reaching high pressures and temperatures when the appliance is subjected to the influence of a source of heat.
The combined effects of the high pressure and temperature levels reached in known pressure cookers enable food to be cooked extremely quickly, while nevertheless ensuring that the organoleptic and nutritional properties of the food are not harmed.
Although such known pressure cookers generally give full satisfaction, they nevertheless put constraints on the user concerning the way cooking is done.
The cooking of food using an appliance of the pressure cooker kind necessarily takes place continuously, i.e. the user cannot take any action directly on the food between the beginning and the end of the cooking process.
In other words, when cooking with a conventional pressure cooker, the user cannot open the lid temporarily while cooking is taking place, at least not in a manner that is simple and quick, for example in order to add ingredients, to taste the food, or more generally to monitor directly how cooking is progressing.
This impossibility for the user to open the lid of conventional pressure cookers while they are cooking, i.e. while the pressure cooker is still subjected to a source of heat, comes from the high level of pressure that exists inside the pressure cooker (relative pressure generally lying in the range 55 kPa to 90 kPa). Directly opening the lid while it is subjected to such pressure levels could lead to the lid being expelled suddenly, possibly together with scalding spray, thereby injuring the user more or less severely.
That is why, prior to any opening of the lid of a conventional pressure cooker, it is necessary to decompress the cooking enclosure, by ceasing to apply heat and by putting the inside of the enclosure into communication with the outside via valve systems provided for this purpose.
Because of the high level of pressure that exists inside the enclosure, the time taken for decompression is nevertheless generally quite long (even if the appliance is put under a stream of cold water), and as a result is incompatible with temporary opening of the lid while cooking is taking place. In addition, known cooking appliances are generally provided with safety systems governing opening that prevent the user from opening the lid of an appliance so long as the pressure inside the appliance is above atmospheric pressure. In order to open the lid, the user must therefore wait for the pressure within the enclosure to become substantially equal to atmospheric pressure; this waiting time is generally lengthy, and prevents known appliances for cooking under pressure being used as a stew pan, i.e. a utensil enabling the lid to be opened temporarily and quickly while cooking is taking place.
Cooking utensils are also known that comprise a bowl and a lid that enables food to be cooked substantially at atmospheric pressure, or at pressures that are slightly higher for certain utensils provided with a regulator valve and a system for locking the lid hermetically relative to the bowl.
Such low-pressure cooking utensils, unlike conventional pressure cookers, do indeed allow the lid to be opened directly and at will during a cooking cycle without it being necessary to begin by performing genuine prior decompression.
Although those utensils do indeed enable the user to open the lid substantially instantaneously while cooking is taking place, they do not provide the advantages associated with genuine pressure cooking, of the kind which takes place in conventional pressure cookers, particularly in terms of speed of cooking and preserving the properties of the food.
Those utensils behave more like somewhat-improved conventional stockpots.